Another step towards getting rid of dependencies to the legacy
pass manager.
Primary change here is to just do -passes=foo instead of -foo in
simple situations (when running a single transform pass). But also
updated a few test running multiple passes.
Also removed some "duplicated" RUN lines in a few tests that where
using both -foo and -passes=foo syntax. No need to do the same kind
of testing twice.
This simplifies the code and fixes handling for the callbr case,
where the instruction needs to be inserted in the normal
destination, rather than after the terminator.
Originally part of D129660.
